Unrelated cord blood transplantation (UCBT) has become a life saving modality of hematopoietic cell transplantation for those cancer patients who lack HLA-matched sibling donors. However, success after UCBT is limited by the high incidence of opportunistic infections (OI), most of which are viral. OI is the major cause of death within the first 6 months, highlighting significant limitations in immune reconstitution. Until thymic recovery ensues, several months post UCBT, protective antiviral immunity depends on the activity of post-thymic T cells infused within the cord blood grafts. However, CB T cells are antigen- inexperienced (naive) lymphocytes that are functionally also limited due to prior exposure to placental factors to protect pregnancy. CB T cells need to undergo in vivo priming, maturation, and peripheral expansion before they could afford protection. Fundamental gaps in knowledge exist regarding the biology and kinetics of developing antigen-specific protective immunity in UCB recipients who also receive immunosuppressive (IS) drugs. In this proposal we will test our central hypothesis that, despite the antigen naivet[unreadable] and immaturity of lymphocytes, successful priming and expansion of protective lymphocyte responses can develop early after UCBT. We also hypothesize that by identifying threshold levels of antigen-specific immunity, we could identify immune correlates of protection. We have developed the tools and scientific strategy to establish novel adoptive cellular therapies applicable to those at high risk to die from OI. Towards these goals we propose three Specific Aims: Aim I: Determine the feasibility of manipulating a small fraction of the cord blood graft to generate a T cell product suitable for adoptive cell therapy without increasing the risk for graft- versus-host disease (GVHD). A small (<5%) fraction of the graft will be first selectively depleted of host- reactive clones then will be exposed to cytokines and CD3/CD28 co-stimulations to expand them to reach clinically relevant numbers and Thl/Tcl maturity, while retaining sufficient diversity. Aim II: Determine the kinetics and clinical relevance of antigen-specific lymphocyte development. Aim II. A: Determine the threshold precursor frequencies for CMV and adenovirus-specific T cells that correlate with protection. Aim II.B: Determine the efficacy of PhageX174 immunization while patients still receive immunosuppression Aim III: Determine the feasibility of ex vivo expanding anti-viral T cells isolated from patients infected with CMV and adenovirus <2 months after UCBT. Clinical translation of the results from these studies will improve survival after UCBT and enhance its applicability with significant public health benefits.